The invention relates to a Coriolis flowmeter. More particularly, the invention relates to a method and apparatus for a Coriolis flowmeter having bi-metallic process connections formed from two dissimilar metals that are metallurgically bonded to form a sealed process connection.
It is known to use Coriolis effect mass flowmeters to measure mass flow and other information of process materials flowing through a pipeline as disclosed in U.S. Pat. No. 4,491,025 issued to J. E. Smith, et al. of Jan. 1, 1985 and Re. 31,450 to J. E. Smith of Feb. 11, 1982. These flowmeters have one or more flow tubes of a straight or a curved configuration. Each flow tube configuration in a Coriolis flowmeter has a set of natural vibration modes, which may be of a simple bending, torsional, radial, or coupled type. Each flow tube is driven to oscillate at resonance in one of these natural modes. The natural vibration modes of the vibrating material filled systems are defined in part by the combined mass of the flow tubes and the process material flowing through the flow tubes. Process material flows into the flowmeter from a connected pipeline on the inlet side of the flowmeter. The process material is then directed through the flow tube or flow tubes and exits the flowmeter to a pipeline connected on the outlet side.
A driver applies a vibrational force to the flow tube. The force causes the flow tube to oscillate. When there is no process material flowing through the flowmeter, all points along the flow tube oscillate with an identical phase. As process material begins to flow through the flow tube, Coriolis accelerations cause each point along the flow tube to have a different phase with respect to other points along the flow tube. The phase on the inlet side of the flow tube lags the driver, while the phase on the outlet side leads the driver.
In an example of a straight tube configuration, a balance bar surrounding the flow tube balances the flow tube and isolates the sensing portion of the flow tube from external influences to provide a specific frame of reference for the sensing portion. Pick off sensors at two different points on the flow tube produce sinusoidal signals representative of the motion of the flow tube at the two points. A phase difference in the two signals received from the sensors is calculated in units of time. The phase difference between the two sensor signals is proportional to the mass flow rate of the process material flowing through the flow tube or flow tubes.
The flow tube and surrounding balance bar are housed in a case. A process connection is connected to each end of the flow tube and to each end of the case. Process connections are fittings that connect the flowmeter to a pipeline or other process material delivery system. A flange is a specific example of a process connection.
In some cases, flowmeters are constructed from dissimilar metals, such as steel and titanium to improve flow meter design. The use of dissimilar metals in flowmeters permits the flowmeters to withstand harsh environments of use such as extreme temperatures, chemical attack, pipeline loading and process pressures. In the context of this application, dissimilar metals are metals that have substantially different properties including hot ductility and coefficients of thermal expansion. The substantially different properties prevent joining of the dissimilar metals by conventional welding techniques.
In one example, a flowmeter case may be constructed from carbon steel and include a stainless steel skin affixed around the exterior surface. The process connections are constructed from stainless steel. The flow tube on the other hand, may be constructed from titanium. Construction of the case from carbon steel, which costs less than stainless steel, lowers manufacturing costs. The stainless steel skin affixed around the case protects the carbon steel from rust and corrosion. The titanium flow tube provides a sanitary metallic flow path for process material.
Different metals have different corrosion tolerances and corrode at varying time intervals. Therefore, it is desirable that process material flowing through the flowmeter only contact a single metal. One prior art method of providing a flow path made of a single metal is to extend the flow tube through the process connection and terminate it flush with the outer edge of the process connection. A titanium insert configured to fit into a recessed portion on the outer face of the process connection is used to join the titanium flow tube to the end of the process connection. The flow tube is welded to the insert by conventional welding techniques. The insert is retained in the recessed portion of the process connection by the weld between the flow tube and the insert. In the prior art the titanium insert is not bonded to the stainless steel process connection. An elastomeric seal, such as an O-ring or silicone, is fitted into the joint between the insert and process connection. This seal is critical because it prevents exterior process materials from leaking into the interior case of the flowmeter.
A first problem with this prior art solution is that the joint between the insert and the process connection is a weak point in the flowmeter. The elastomeric seal breaks down at a faster rate than other surrounding welded joints. This results in a premature failure of the flowmeter because the seal cannot be replaced without destroying the entire flowmeter.
A second problem with this prior art solution is that the joint between the titanium insert and the stainless steel process connection also fails prematurely due to galvanic corrosion, resulting in premature meter failure. Furthermore, the galvanic corrosion is accelerated where the process material is corrosive.
A third problem with this prior art solution is present in applications where the flowmeter case is relied on to provide a secondary containment for the process material in the event the flow tube fails. The O-ring seal or other elastomeric seal is not designed to handle such process material, especially in large pressurized volumes present during a flow tube failure. This problem is further compounded by the fact that the need for secondary containment typically arises during applications where the process material is highly corrosive or toxic.
The above and other problems are solved and an advance in the art is made by the method and apparatus of the invention wherein a bi-metallic process connection made from a first metal and a dissimilar metal that are metallurgically bonded to form a sealed process connection for a Coriolis flowmeter. A first advantage is that the need for an elastomeric seal is eliminated. A second advantage is that the bonded first metal and dissimilar metal provide superior corrosion resistance. This extends the useful life of the flowmeter in highly corrosive environments.
A Coriolis flowmeter embodying the method and apparatus of the invention includes at least one flow tube made of a first metal and a process connection made of the first metal metallurgically bonded to a dissimilar metal to form a sealed structure. A central aperture extends through the process connection and is enclosed by at least a portion of the first metal in the process connection. An end of the flow tube is affixed to the first metal in the process connection to provide a flow path enclosed by the first metal.
A first exemplary embodiment of the present invention is a stainless steel flange that includes a titanium insert metallurgically bonded to a first end of the flange. The flange includes a central recessed portion in the first and that connects to the pipeline. The central recessed portion circumscribes a central aperture passing through the main body of the flange. The recessed portion is configured to receive a cylindrical titanium insert that has a central aperture configured to mate with the central aperture of the flange. The titanium insert is metallurgically bonded into the central recessed portion of the flange to form a sealed process connection of the present invention. A second end of the flange is welded to the end of the stainless steel flowmeter case by conventional welding techniques. The titanium flow tube is welded to the titanium insert by conventional welding techniques to form a flow path enclosed by a single metal.
In a second possible exemplary embodiment of the present invention the insert includes a stainless steel first face and a titanium second face metallurgically bonded to form a composite stainless steel/titanium insert. The stainless steel portion of the insert is welded in the recessed portion of the main body by conventional welding techniques and the titanium portion of the insert is welded to the titanium flow tube by conventional welding techniques.
In a third possible exemplary embodiment of the present invention, the process connection comprises a sanitary fitting made of titanium and stainless steel. A titanium face is metallurgically bonded to a stainless steel first end of the process connection to form a sealed process connection of the present invention. The stainless steel end of the sanitary fitting is welded to the stainless steel flowmeter case by conventional welding techniques. The flow tube extends through the process connection and is welded to the titanium face of the sanitary fitting by conventional welding techniques to form a flow path enclosed by a single metal.
Aspects of the invention include a method and apparatus defining a Coriolis flowmeter comprising at least one flow tube formed from a first metal;
a balance bar coaxial with said at least one flow tube and having ends connected to said at least one flow tube to partially enclose said at least one flow tube;
a driver coupled to said at least one flow tube and said at least one balance bar to vibrate said at least one flow tube and said at least one balance bar in phase opposition;
sensors affixed to said at least one flow tube to measure oscillations and transmit information about said oscillations to meter electronics responsive to said driver vibrating said at least one flow tube and at least one balance bar;
a process connection formed from said first metal and at least one dissimilar metal metallurgically bonded to said first metal;
an aperture through said process connection from a second end that connects to a case to a first end that connects to a pipeline wherein said first metal of said process connection encloses at least a portion of said aperture; and
an end of said at least one flow tube affixed to said first metal of said process connection enclosing said aperture to provide a flow path enclosed by said first metal.
A second aspect of the invention includes a Coriolis flowmeter wherein said process connection is a flange further comprising an insert bonded to said first end of said aperture to form said sealed structure.
A third aspect of the invention includes a Coriolis flowmeter further comprising a recessed portion around said aperture on said first end of said process connection that receives said insert.
A fourth aspect of the invention includes a Coriolis flowmeter wherein said at least one flow tube extends through said aperture of said process connection from said second end to said first end and connects to said insert.
A fifth aspect of the invention includes a Coriolis flowmeter wherein said insert is bonded to said process connection to form said sealed structure by brazing.
A sixth aspect of the invention includes Coriolis flowmeter wherein said insert is a bi-metallic insert formed by explosion bonding.
A seventh aspect of the invention includes a Coriolis flowmeter wherein said bi-metallic insert is bonded to said process connection to form said sealed structure by conventional welding techniques.
A eighth aspect of the invention includes a Coriolis flowmeter wherein said insert is bonded to said process connection to form said sealed structure by projection welding.
A ninth aspect of the invention includes a Coriolis flowmeter wherein said insert is bonded to said process connection to form said sealed structure by inertia welding.
A tenth aspect of the invention includes a Coriolis flowmeter wherein the process connection is a sanitary fitting.
An eleventh aspect of the invention includes a Coriolis flowmeter wherein said sanitary fitting comprises a face formed from said first metal;
a main body formed from said at least one dissimilar metal, and
said face and said main body are bonded together to form said sealed structure and define said aperture.
A twelfth aspect of the invention includes a Coriolis flowmeter wherein said first metal is titanium.
A thirteenth aspect of the invention includes a Coriolis flowmeter wherein said dissimilar metal is stainless steel.
A fourteenth aspect of the invention includes a Coriolis flowmeter wherein said face of said sanitary fitting and said main body of said sanitary fitting are bonded together to form said sealed structure by explosion bonding.
A fifteenth aspect of the invention includes a Coriolis flowmeter wherein said face of said sanitary fitting and said main body of said sanitary fitting are bonded together to form said sealed structure by brazing.
A sixteenth aspect of the invention includes a Coriolis flowmeter wherein said face of said sanitary fitting and said main body of said sanitary fitting are bonded together to form said sealed structure by projection welding.
A seventeenth aspect of the invention includes a Coriolis flowmeter wherein said face of said sanitary fitting and said main body of said sanitary fitting are bonded together to form said sealed structure by inertia welding.